Although agile development methods have been around for a little while now, many people still ask about the agile development cycle, what it is and how exactly it’s different to a more traditional approach to development projects. Here is a simple explanation of the basics for people new to all this.
Traditional software development projects follow what is commonly known as a waterfall approach, where each phase of the software development life cycle is completed in detail and in sequence, one stage at a time. Simplistically a traditional software development life cycle might look something like this…
‘Waterfall’ Software Development Life Cycle (SDLC)
Each phase is completed in turn, for instance:
With waterfall projects, the whole project is analysed, then designed, then developed, then tested, and then deployed. Sometimes projects are cut into multiple smaller phases to make them more manageable, but still these phases tend to work roughly sequentially like above and tend to still be quite large, for instance 3-6 months or maybe even more.
Agile Development Cycle
An agile development cycle is different. Instead, the initial planning and analysis is kept to a very high level, just enough to outline the scope of the development project. Then the team go through a series of iterations, analysing, designing, developing and testing each feature in turn within the iterations.
For instance, it might look a bit more like this:
There aren’t really any distinct stages during the development. Instead, each feature is taken from start to finish within an iteration, with the software being released at the end of each iteration, or if appropriate even during an iteration.
An iteration is simply a fixed, short period of time that the team chooses to work within. Typically for agile teams, an iteration is between 1 week and 30 days. Strictly speaking, the Scrum agile development methodology advocates 30 days, but I’ve encountered very few teams that actually do this. 2 or 3 weeks seems to be more common. The Extreme Programming agile methodology advocates 1 week. This is very short and in my experience requires quite a lot of maturity in the team and its processes to achieve, because getting to a stable release every week can be difficult.
Either way, the principles are the same. The idea is to stick to short, fixed-length iterations and complete all stages of the development cycle for each feature in turn within an iteration.
The key difference this creates is visibility of complete working features much earlier in the project life cycle, allowing for a better gauge of progress and quality, and allowing for feedback and adaption along the way. The result is to see some results earlier, mitigate risk, and to allow flexibility to accommodate change.
One of the dangers of a waterfall approach is that by the time the detailed up-front planning, analysis and design are done, let alone by the time the solution is developed and tested, many requirements may have changed – especially these days when the pace of change is so incredibly fast. Agile mitigates this risk too, helping to ensure that the right solution is delivered.